1. Field of the Invention
This invention pertains to driver circuits for driving multiple quantum well modulators in high density electronic chips having a combination of electronic and optic devices. More particularly, the present invention pertains to driver circuits for increasing the voltage range across multiple quantum well modulators while limiting the maximum voltage applied across the transistors in the modulator driver circuit.
2. Description of the Related Art
Electronic chips having a combination of electronic and optic circuits for use in, among other things, optic communication systems in computers, are known. Typically, such electronic chips employ at the transmitter stage driver circuits which are comprised of field effect transistor (FET) configurations for driving normal incidence multiple quantum well (MQW) modulators, as described in U.S. Pat. No. 5,289,015. The MQW modulators output optical signals which are detected by an optical receiver. The optical signals generated by an MQW modulator are related to the voltage applied across the terminals of the modulator via the electric field generated by that voltage within the MQW region, as described in U.S. Pat. No. 4,716,449. Thus, for example, in one mode of operation if a low voltage is applied across an MQW modulator, most of the normal incident light will be reflected, thus corresponding to a logic "0". If a high voltage is applied across an MQW modulator, most of the normal incident light will be absorbed, thus corresponding to a logic "1".
When using MQW modulators in such driver transmitter circuits, it is desirable to increase the voltage range across the MQW modulators because this will permit the use of modulators having superior optical performance as compared to devices of the same class whose operating voltage is restricted. For example, in addition to an increased tolerance to temperature variation, an increased contrast between the optical signals corresponding to a logic "0" and those corresponding to a logic "1" can be obtained. This translates into a more precise and higher certainty distinction between the dark and light optical signals corresponding to a logic "1" and a logic "0". However, increasing the voltage range across an MQW modulator has several drawbacks. Specifically, if the increased maximum voltage across the MQW modulator is beyond the breakdown voltage of conventional FETs, the circuit may fail due to catastrophic damage to the FETs. On the other hand, if FETs having increased breakdown voltages are used, FET performance will be reduced and manufacturing yield may be compromised. Thus, it is desirable to have an increased voltage range across the MQW modulators in a transmitter driver circuit without increasing the voltages applied to the FETs in the associated driver circuit.
Accordingly, it is an object of the present invention to provide a transmitter driver circuit that applies an increased voltage range to the modulator while limiting the maximum voltage applied across the associated transistors.
It is a further object of the invention to provide a differential transmitter driver circuit for comparing the optical signal generated by a first modulator to the optical signal generated by a second modulator.
Other objects and features as well as additional details of the present invention will become apparent from the following detailed description and annexed drawings of the presently preferred embodiments thereof, when considered in conjunction with the associated drawings.